Mine may have been a bit different situation. I was doing off-site meetings at my boss's house (I'm a remote employee a couple hundred miles from the office) so the sitter came to the home and watched DS in another room in the house. I used care.com and sittercity to find them.
If the conference is at a hotel, maybe the concierge could help find someone. It may not be the right idea this time, but maybe for the future.